Oil removal device

ABSTRACT

A buoyant oil-removal device for use with a floating oilconfining barrier on a water surface with oil slicks of substantial thickness floating thereon, the device having oil inflow ports (of lesser vertical height than the oil slick thickness) with the ports normally floated at a level intermediate the thickness of the oil slick to provide inflow of the water-floated oil slick and to minimize either water or air inflow through said ports whether the water is calm or disturbed by waves, and designed to collect oil from the water surface at a rate which is maximized subject to the requirement that intake of water and air is minimized. The device has a longest overall dimension of not more than one-fourth of the wavelength of the shortest wave of significant amplitude, and includes a generally H-shaped skimmer structure; each arm portion of the structure is of generally rectangular or circular cross section, providing a plurality of inflow ports, each of vertical dimension of the order from 0.04 to 0.2 of the expected slick thickness. Inflow ports preferably are positioned immediately adjacent the top surface of the structure, and are horizontally elongated. The device is provided with a flexible, buoyant suctioning hose communicating with the inflow ports for the removal of oil.

United States Patent Cross, III

[54] OIL REMOVAL DEVICE |72| Inventor: Ralph Herbert Cross, III,Lexington,Mass.

[731 Assignees: David Parks Hoult, Wellesley; Ralph 11. Cross, 111,Lexington; Jerome ll. Milgram, Cambridge, Mass.

[22] Filed: March 12, 1971 [21] Appl. No.1 123,567

[52] US. Cl ..210/242, 2lO/DIG. 21 [51] Int. Cl. ..C02b 9/02 [58] Fieldof Search ..210/83, 242, DIG 21 [56] References Cited UNITED STATESPATENTS 2,891,672 6/1959 Veld et al ..2l0/242 3,22l,884 l2/l965Mulle'r...., ..2l0/242 FOREIGN PATENTS OR APPLICATIONS 1 1,528,7776/1968 France ..2l0/DIG. 2l

Primary Examiner-Reuben Friedman Assistant Examiner-T. A. GrangerAttorney-Martin Kirkpatrick 1451 Dec. 19, 1972 [57} ABSTRACT A buoyantoil-removal device for use with a floating oil-confining barrier on awater surface with oil slicks of substantial thickness floatingthereon,- the device having oil in-flow ports (of lesser'vertical heightthan the oil slick thickness) with the portsnormally floated at a levelintermediate the thickness of the oil slick to provide inflow of thewater-floated oil slick and to minimize either water or air inflowthrough said ports whether the water is calm or disturbed by waves, anddesigned to collect oil from the water surface at a rate which ismaximized subject to the requirement that intake of water and air isminimized. The device has a longest overall dimension of not more thanone-fourth of the wavelength of the shortest wave of significantamplitude, and includes a generally H-shaped skimmer.

structure; .each arm portion of the structure is of generallyrectangular or circular cross section, providing a plurality of inflowports, each of vertical dimen-v sion of the order from 0.04 to 0.2 ofthe'expected slick thickness. Inflow ports preferably are positionedimmediately adjacent the top surface of the structure, and arehorizontally elongated. The device is provided with a flexible, buoyantsuctioning hose communicating with the inflow ports for the removal ofoil.

5 Claims, 4 Drawing Figures PATENTEU 19 I97? 3 706, 382

SHEET 2 OF 2 I lllllllllllllllll l 1 on. REMOVAL DEVICE This inventionrelates to the removal of oil from the surface of water. I

Often, the problem of removing spilled oil occurs on the open sea, as aresult of damage to an oil tanker or the like. The escaping oil may beprevented from spreading by confining it within any of various types ofbarriers, such as the one described in copending applications Ser. No.54,530 and Ser. No. 79,051. However, the oil must then be removed fromthe water.

Many devices-have been developed to remove such oil but. usually admixedwith a substantial amount-of water, including selectively wettableendless belts, skimmer boats, sorbents, and similar devices. In general,these devices provide only limited flow rates of oil, and usually theymust be moved by, mounted on, or constructed as an integral part of, avessel. These characteristics render most such devices unsatisfactory.Also, the problem is in general complicated by the presence of constantsurface waves, which cause the collection device to move verticallythrough the oil slick, in and out of the water and air. This makes itdifficult to maintain a continuous flow of oil into the device and alsoresults in the entrainment of a good deal of water. Additionally, ifwaves are generally reflected from the device, oil will be carried awayfrom it and cannot be removed.

It is therefore an object of this invention to provide an oil-removaldevice that permits a satisfactory rate of oil intake, and that need notbe moved by, mounted on, or constructed as part of a vessel. It is afurther object to provide such a device that is able to follow most wavedisturbances of significant magnitude and thereby is able to maintain agenerally uninterrupted flow of oil, even on the open ocean, and thatcauses minimum reflection of incident waves. The significant wave heightis commonly defined as the average height of the highest one-third ofall the waves in a record. A wave which will significantly affect theperformance of the oil removing device has a height generally in excessof the oil slick thickness, and a length generally exceeding ten timesthat height.

A buoyant oil-removal device that draws the oil by suction throughin-flow ports can provide a satisfactory I rate of flow. However, whenfluid is drawn through such ports, as a result of flow conditions at theports, as the rate of flow increases, the quantities of air and waterentrained and drawn into the device tend to increase also. Such air andwater must then be separated from the oil, and the efficiency of suchdevices is much impaired. Moreover, this problem occurs even in theabsence of large-scale wave disturbances.

It is therefore another object of this invention to provide an efficientoil-removal device capable of maximizing the rate and amount of oil flowwhile minimizing the relative quantities of air and water entrained withthe oil.

Further, it is an object to provide such an oil-removal device that issimple and inexpensive to construct and reliable in operation.

The invention in its preferred form features a buoyant oil-removaldevice, normally for use with a floating oil-confining barrier on awater surface with oil slicks of substantial thickness floating thereon,the device having in-flow ports of lesser vertical height than the oilslick thickness, normally continuously floated at a level within'thethickness of the oil slick. In preferred embodiments, the deviceincludes an H- shaped skimmer structure, consisting of a cross memberand two arm portions; each arm portion of the structure is of generallyrectangular or circular cross section and provides a plurality of inflowports each of vertical dimension of the order of 0.04 to'O.2 of theexpected slick thickness, positioned immediately adjacent the topsurface of the oil and horizontally elongated. A flexible buoyantsuction hose communicates through the structure with the inflow portsfor the removal of oil. Buoyancy means are provided in the form of afloat frame, from which the skimmer may be suspended, and float elementssuspended from the frame outboard of the skimmer. The longest dimensionof the entire device is preferably not more than onefourth thewavelength of the shortest waves whose amplitude is significant indisturbing. the device, and preferably less, permitting the device tomove substantially with the water surface under the action of suchwaves, thereby normally continuously maintaining the inflow portsgenerally within the oil slick thickness.

Other objects, features and advantages will appear from the followingdescription of a preferred embodiment of the invention, taken togetherwith theattached drawings thereof, in which:

FIG. 1 is a perspective view of a preferred embodiment of theoil-removal device of the invention;

FIG. 2 is a view of the skimmer portion of the device of FIG. 1;

FIG. 3 is a view of an alternative form of the skimmer portiomand FIG. 4is a schematic view of flow conditions near an inflow port.

Referring now to the drawings, and particularly to FIG. 1, theoil-removal device 10 includes a generally H-shaped skimmer portion 12,of generally rectangular cross-section. The choice of an H-shape for theskimmer manifold is not critical, but provides a compact structure withrelatively short arms, thereby ensuring a relatively small pressure dropover the length of the arm. The cross-sectional area of the arms 14 and16 generally increases from the free ends toward crosspiece 18. A hosefitting 20 is provided in cross-piece 18, positioned immediatelyadjacent top surface 22 of skimmer l2. ln-flow ports 24 in the form ofslots are provided along the inner and outer sides of arms 14 and 16.Further slots 26 are provided in the ends of arms 14 and' 16, but noneare provided on cross-piece 18, for reasons that will appear more fullyin what follows.

Skimmer 12 is preferably constructed of 96 inch thick aluminum alloy5086, intended for marine use; seams may be welded or riveted, and thetop or bottom plates may be bolted to the rest of the skimmer 12 tosimplify cleaning after use. v i

The purpose of the top plate on the device is to control the pressuregradient in the flow of oil within the i060" (DSI be entrained at theentrance to the hose. The bottom plate performs a similar function withrespect to the oilwater interface.

Four frame-mounting plates 28 are provided for attaching the floatframe. Float frame 30 is constructed of aluminum alloy structuralsections. Two angle sections 32 and 34 are welded to two channelsections 36 and 38. Skimmer 12 is bolted to channel sections 36 and 38through frame-mounting plates 28, using long studs to allow adjustmentof the vertical position of the skimmer 12. Float mounting plates 40 arefastened to the free ends of angle' sections 32 and 34.

The floats 42 may be closed cell foam blocks, with plywood sections 44bonded to the top and bottom of the foam for strength. Floats 42 arebolted to float mounting plates 40 with stainless steel bolts orthreaded rod. The choice of spaced float elements, rather than a singlebuoyant skimmer, results in a device that presents a small reflectingarea to incident waves. Thus waves tend to move past the skimmer,carrying the oil slick with them past the inflow ports. This choice alsoprovides superior wave-following ability, as described below.

In order to keep the oil fraction of the oil-water mixture removed bythe skimmer relatively high enough for the device to be practical, theskimmer inflow ports must follow the motion of the free surface. Thisrequires that the skimmer heave and roll in unison with the freesurface. Therefore, the natural frequencies of the heave and rollmotions must be at least twice as high as the frequencies of most of thewaves and the physical dimensions of the entire device must be muchsmaller than the lengths of most of the waves.

As a practical matter, if the oil slick is, e.g., V4 foot to 1 footthick, as it may be if concentrated by a barrier, waves shorter thanabout 30 feet, crest tocrest, do not interfere significantly with theoperation of the device. Waves of this length have a height of about 2feet or so and a period of about 2.7 seconds.

Therefore, the physical length and width dimensions of the device shouldnot exceed 10 feet and the natural periods in heave and roll should beless than 1.4 seconds. If such devices do not have enough collectioncapacity, a number of them must be used instead of increasing the sizeof a single device so much that it does not follow the waves. well.

In the preferred embodiment described here, the over-all length of thedevice, from the outer edge of one float 42 to the outer edge of thenext, is 66 inch or 5.5 feet. This length is suitable for use inconditions in which the significant wave height considered is about 5feet, corresponding to a wavelength of about 40 to 70 feet. Thus thelength of the device is about one-eigth of the shortest wavelengthconsidered, permitting the device to respond well to most surfacemotions. The entire unit weighs about l pounds.

The cross-sectional area of the arms increases from inches X 2.5 inchesat the outer ends to 5 inches X 5 inches at the cross-piece, whichcauses the flow velocity at the center to be about one-half the inletvelocity. This tapered structure assists in the control of entrainedair, and enhances the wave response.

The over-all dimensions of the device have been determined to ensurethat ports 24 and 26 are maintained within the oil slick thickness asubstantial portion of the time. Further theoretical considerationsdetermine the dimensions of the ports themselves.

The maximum velocity at which oil floating on water can be drawn throughan orifice or slot is limited by two phenomena: the entrainment of airfrom the surface, and the entrainment of water from below. Referring toFIG. 4, the Venturi efi'ect at the slot draws the air-oil interfacedownward and the water-oil interface upward, and thus vertically thinsdown the slick locally. Because this effect occurs at the ports on theinner sides of arms 14 and 16, if ports were placed on the cross-piece18 of the skimmer, the slick would be so thinned locally that more waterand air than oil would be drawn into the skimmer. Moreover, the pressureinside cross-piece 18 is lower than in arms 14 and 16, and thus inflowthrough ports in the cross-piece would be morelikely to entrain air orwater. Therefore, no ports are placed on the cross-piece.

The thinning down of the slick near the ports depends on the velocity offlow through the ports. Treating the inlet as having no vertical extent,and letting h be the depth of the inlet below the undisturbed air/oilinterface, the inlet oil velocity at which air begins to be entrainedwith the oil may be calculated by applying the steady-state energy(Bernoullis) equation for irrotational flow, giving uir Similarly,letting h be the depthof the undisturbed oil/water interface belowtheinlet, the same equation gives for the inlet oil velocity at which waterbegins to be entrained wuler the maximum inlet velocity without air orwater entrainment when the inlet is located at a depth h below theair/oil interface and h above the water/oil interface is given by A V=(2g h Thus, the maximum velocity at which oil can be drawn into aninlet port without entrainment of air or water depends on the specificgravity of the oil (through A) and the local (undisturbed) oil slickdepth h ln practice, the inlet port is not of zero height, but has avertical height S which must be subtracted from the local thickness, asentrainment of air begins at its top edge and entrainment of water atits lower edge. Since the maximum inlet velocity is fixed, the totalrate of flow of oil will depend on the total inlet area, which is aproduct of the number of inlet ports, and the width and height of each.Two practical considerations affect the choice of slot height S. First,as oil is removed from the confined pool, the thickness of the pooldecreases. Thus, if the value of S is chosen to be an appreciablefraction of the initial thickness of the slick h,,, while the initialflow rate will be large, the entrainment of air and water will become aserious problem before the oil pool is entirely removed. Also, if S isan appreciable fraction of h,,, small deviations in the position of theslot, caused for example by buoyancy changes as the pool is exhausted,or by small waves, will cause entrainment of air or water. Theseconsiderations lead to the choice of a value of S that is much smallerthan the expected slack thickness. In practice, it has been found thatfor a slick 1 foot thick, a slot height S of 7% inch to 1% isappropriate.

In practice, the flow rate of oil through the device can be such thatthe velocity through each and every orifice is less than V max. In suchoperation, less than the maximum rate of oil collection is achieved, butmy theory and experiments have shown that very little water or air isentrained in the oil.

However, since the horizontal spacing between ports along the skimmerdoes not influence entrainment, elongated holes, or slots, can be used,with essentially minimum spacing between adjacent slots, to obtain thedesired flow rate. Such an arrangement of slots is shown in FIG. 1. Theslots are placed adjacent top surface 22 of skimmer 12 to assist in thecontrol of entrained air.

An oil-removal device constructed as shown in FIG. 1 is conservativelydesigned to collect 5 tons of oil per hour, from an oil pool initiallyabout 1 foot deep when the value of A is 0.10. For a slick 1 foot thick,with waves and a current, a ratio of oil to total fluid collected of 0.9can be expected in 3 foot waves, and 0.80 or better in 5 foot waves,using properly selected pumps and hoses, and with proper operation ofthe entire system. A suitable suctioning means for use with the deviceof FIG. 1 may comprise a non-emulsifying, self-priming pump or pumps(such as a double Edson diaphragm pump) with variable speed control;using such equipment, the velocity in each inlet port is less thanV,,,,,,,, and no valves are required to control this velocity.

The oil-removal device of the present invention is operable when thereis a current in the water of as much as, say, 2 knots, and theefficiency of the device may even be increased, as the device may beoriented so that the current carries oil to the skimmer and concentratesit in a deep pool for collection. Thedevice may be readily oriented, asdesired, to take account of current, wave and wind conditions bytethering or anchor lines, adjusted to suit.

While a skimmer with rectangular cross-section has been described, onehaving a circular cross-section, as shown in FIG. 3, may also beemployed. Alternatively, inlet ports may be located in the horizontaltop surface of the skimmer, rather than in the side walls; the flowthrough the ports is not significantly altered by such an arrangement solong as the hole is located a distance h down from the top of the oilsurface.

The vertical position of the inlet ports, as well as the verticaldimension, may be made adjustable if desired for use in varyingconditions. In the embodiment described here, this adjustment may beprovided by double nuts on the long-threaded studs connecting plates 28on the skimmer 12 to the channels 36,38 on the flotation structure 30.Alternative] interch ble side walls for skimmer 12 could pr vide inle tp o i' t s of various slot heights or vertical position.

What is claimed is:

1. In a buoyant oil-removal device for use on a water surface with anoil slick of substantial thickness floating thereon, a generallyH-shaped skimmer structure adapted and arranged to be water-floatedhaving a plurality of oil-inflow ports disposed around arms of saidH-shaped structure with said ports normally floated at a level withinsaid oi] slick,

separate buoyancy means attached to said skimmer structure for floatingthe same,

and conduit means attached to the cross-piece of said I-I-shapedstructure communicating with said ports for withdrawing oil collectedfrom said water surface, whereby said device floats generally parallelto said water surface both when said surface is calm and when it isdisturbed by waves, normally maintaining said ports substantially at alevel within said oil slick, thus providing a maximum ratio of withdrawnoil to entrained withdrawn air andv water.

2. The device of claim 1 wherein the cross-section of each arm of saidH-shaped skimmer structure is generally rectangular, the area of saidcross-section generally increasing from each end of said arms towardsaid cross-piece.

3. In a buoyant oil-removal device for use on a water surface with anoil slick of substantial thickness floating thereon, a generallyH-shaped skimmer structure adapted and arranged to be water-floatedhaving a plurality of oil-inflow ports with said ports normally floatedat a level within said oil slick,

separate buoyancy means including float elements and a float frameattached to said skimmer structure for floating the same, said H-shapedskimmer structure being suspended from said float frame, and said frameproviding float-suspending portions spaced from said H-shaped structure,said float elements being suspended therefrom,

the longest dimension of said device being the distance from one saidfloat element to an adjacent said float element, including the length ofsaid float elements, and conduit means communicating with said ports forwithdrawing oil collected from said water surface,

whereby said device floats generally parallel to said water surface bothwhen said surface is calm and when it is disturbed by waves, normallymaintaining said ports substantially at a level within said oil slick,thus providing a maximum ratio of withdrawn oil to entrained withdrawnair and water.

4. The device of claim 3 wherein the vertical dimension of said inflowports is adjustably fixed.

5. The device of claim 3, wherein the vertical distance between saidfloat elements and said inflow ports is adjustably fixed.

l060ll 0033

1. In a buoyant oil-removal device for use on a water surface with anoil slick of substantial thickness floating thereon, a generallyH-shaped skimmer structure adapted and arranged to be water-floatedhaving a plurality of oil-inflow ports disposed around arms of saidH-shaped structure with said ports normally floated at a level withinsaid oil slick, separate buoyancy means attached to said skimmerstructure for floating the same, and conduit means attached to thecross-piece of said H-shaped structure communicating with said ports forwithdrawing oil collected from said water surface, whereby said devicefloats generally parallel to said water surface both when said surfaceis calm and when it is disturbed by waves, normally maintaining saidports substantially at a level within said oil slick, thus providing amaximum ratio of withdrawn oil to entrained withdrawn air and water. 2.The device of claim 1 wherein the cross-section of each arm of saidH-shaped skimmer structure is generally rectangular, the area of saidcross-section generally increasing from each end of said arms towardsaid cross-piece.
 3. In a buoyant oil-removal device for use on a watersurface with an oil slick of substantial thickness floating thereon, agenerally H-shaped skimmer structure adapted and arranged to bewater-floated having a plurality of oil-inflow ports with said portsnorMally floated at a level within said oil slick, separate buoyancymeans including float elements and a float frame attached to saidskimmer structure for floating the same, said H-shaped skimmer structurebeing suspended from said float frame, and said frame providingfloat-suspending portions spaced from said H-shaped structure, saidfloat elements being suspended therefrom, the longest dimension of saiddevice being the distance from one said float element to an adjacentsaid float element, including the length of said float elements, andconduit means communicating with said ports for withdrawing oilcollected from said water surface, whereby said device floats generallyparallel to said water surface both when said surface is calm and whenit is disturbed by waves, normally maintaining said ports substantiallyat a level within said oil slick, thus providing a maximum ratio ofwithdrawn oil to entrained withdrawn air and water.
 4. The device ofclaim 3 wherein the vertical dimension of said inflow ports isadjustably fixed.
 5. The device of claim 3, wherein the verticaldistance between said float elements and said inflow ports is adjustablyfixed.